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Subject: Re: [PATCH 5/5] x86/mm/kaiser: Disable the SYSCALL-64 trampoline
 along with KAISER
To: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org
References: <20171127223110.479550152@infradead.org>
 <20171127223405.381212307@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, daniel.gruss@iaik.tugraz.at,
        hughd@google.com, keescook@google.com, linux-mm@kvack.org,
        michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
        richard.fellner@student.tugraz.at
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <dffd1146-5cc5-ae14-ec10-3df312703790@linux.intel.com>
Date: Mon, 27 Nov 2017 14:53:43 -0800
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On 11/27/2017 02:31 PM, Peter Zijlstra wrote:
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1442,7 +1442,10 @@ void syscall_init(void)
>  		(entry_SYSCALL_64_trampoline - _entry_trampoline);
>  
>  	wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
> -	wrmsrl(MSR_LSTAR, SYSCALL64_entry_trampoline);
> +	if (kaiser_enabled)
> +		wrmsrl(MSR_LSTAR, SYSCALL64_entry_trampoline);
> +	else
> +		wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);

Heh, ask and ye shall receive, I guess.

We do need a Documentation/ update now.  For this, and other things.
I'll put something together.